---
description: Monitor files and directories in real-time to build responsive development tools and automation workflows.
title: Watch filesystem changes
image: https://developers.cloudflare.com/og-docs.png
---

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# Watch filesystem changes

Last updated Aug 24, 2026|Copy as Markdown|[View as Markdown](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/file-watching/index.md)|[Agent setup](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/agent-setup/)

This guide shows you how to monitor filesystem changes in real-time using the Sandbox SDK's file watching API. File watching is useful for building development tools, automated workflows, and applications that react to file changes as they happen.

The `watch()` method returns an SSE (Server-Sent Events) stream that you consume with `parseSSEStream()`. Each event in the stream describes a filesystem change.

## Basic file watching

Start by watching a directory for any changes:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
		console.log(`Is directory: ${event.isDirectory}`);
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
		console.log(`Is directory: ${event.isDirectory}`);
	}
}
```

The stream emits four lifecycle event types:

* **`watching`** — Watch established, includes the `watchId`
* **`event`** — A filesystem change occurred
* **`error`** — The watch encountered an error
* **`stopped`** — The watch was stopped

Filesystem change events (`event.eventType`) include:

* **`create`** — File or directory was created
* **`modify`** — File content changed
* **`delete`** — File or directory was removed
* **`move_from`** / **`move_to`** — File or directory was moved or renamed
* **`attrib`** — File attributes changed (permissions, timestamps)

## Filter by file type

Use `include` patterns to watch only specific file types:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

// Only watch TypeScript and JavaScript files
const stream = await sandbox.watch("/workspace/src", {
	include: ["*.ts", "*.tsx", "*.js", "*.jsx"],
});

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

// Only watch TypeScript and JavaScript files
const stream = await sandbox.watch("/workspace/src", {
	include: ["*.ts", "*.tsx", "*.js", "*.jsx"],
});

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
	}
}
```

Common include patterns:

* `*.ts` — TypeScript files
* `*.js` — JavaScript files
* `*.json` — JSON configuration files
* `*.md` — Markdown documentation
* `package*.json` — Package files specifically

## Exclude directories

Use `exclude` patterns to skip certain directories or files:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace", {
	exclude: ["node_modules", "dist", "*.log", ".git", "*.tmp"],
});

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		console.log(`Change detected: ${event.path}`);
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace", {
	exclude: ["node_modules", "dist", "*.log", ".git", "*.tmp"],
});

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		console.log(`Change detected: ${event.path}`);
	}
}
```

Default exclusions

The following patterns are excluded by default: `.git`, `node_modules`, `.DS_Store`. You can override this by providing your own `exclude` array.

## Build responsive development tools

### Auto-rebuild on changes

Trigger builds automatically when source files are modified:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src", {
	include: ["*.ts", "*.tsx"],
});

let buildInProgress = false;

for await (const event of parseSSEStream(stream)) {
	if (
		event.type === "event" &&
		event.eventType === "modify" &&
		!buildInProgress
	) {
		buildInProgress = true;
		console.log(`File changed: ${event.path}, rebuilding...`);

		try {
			const result = await sandbox.exec("npm run build");
			if (result.success) {
				console.log("Build completed successfully");
			} else {
				console.error("Build failed:", result.stderr);
			}
		} catch (error) {
			console.error("Build error:", error);
		} finally {
			buildInProgress = false;
		}
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src", {
	include: ["*.ts", "*.tsx"],
});

let buildInProgress = false;

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (
		event.type === "event" &&
		event.eventType === "modify" &&
		!buildInProgress
	) {
		buildInProgress = true;
		console.log(`File changed: ${event.path}, rebuilding...`);

		try {
			const result = await sandbox.exec("npm run build");
			if (result.success) {
				console.log("Build completed successfully");
			} else {
				console.error("Build failed:", result.stderr);
			}
		} catch (error) {
			console.error("Build error:", error);
		} finally {
			buildInProgress = false;
		}
	}
}
```

### Auto-run tests on change

Re-run tests when test files are modified:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/tests", {
	include: ["*.test.ts", "*.spec.ts"],
});

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event" && event.eventType === "modify") {
		console.log(`Test file changed: ${event.path}`);
		const result = await sandbox.exec(`npm test -- ${event.path}`);
		console.log(result.success ? "Tests passed" : "Tests failed");
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/tests", {
	include: ["*.test.ts", "*.spec.ts"],
});

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event" && event.eventType === "modify") {
		console.log(`Test file changed: ${event.path}`);
		const result = await sandbox.exec(`npm test -- ${event.path}`);
		console.log(result.success ? "Tests passed" : "Tests failed");
	}
}
```

### Incremental indexing

Re-index only changed files instead of rescanning an entire directory tree:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/docs", {
	include: ["*.md", "*.mdx"],
});

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		switch (event.eventType) {
			case "create":
			case "modify":
				console.log(`Indexing ${event.path}...`);
				await indexFile(event.path);
				break;
			case "delete":
				console.log(`Removing ${event.path} from index...`);
				await removeFromIndex(event.path);
				break;
		}
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/docs", {
	include: ["*.md", "*.mdx"],
});

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		switch (event.eventType) {
			case "create":
			case "modify":
				console.log(`Indexing ${event.path}...`);
				await indexFile(event.path);
				break;
			case "delete":
				console.log(`Removing ${event.path} from index...`);
				await removeFromIndex(event.path);
				break;
		}
	}
}
```

## Advanced patterns

### Process events with a helper function

Extract event processing into a reusable function that handles stream lifecycle:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

async function watchFiles(sandbox, path, options, handler) {
	const stream = await sandbox.watch(path, options);

	for await (const event of parseSSEStream(stream)) {
		switch (event.type) {
			case "watching":
				console.log(`Watching ${event.path}`);
				break;
			case "event":
				await handler(event.eventType, event.path, event.isDirectory);
				break;
			case "error":
				console.error(`Watch error: ${event.error}`);
				break;
			case "stopped":
				console.log(`Watch stopped: ${event.reason}`);
				return;
		}
	}
}

// Usage
await watchFiles(
	sandbox,
	"/workspace/src",
	{ include: ["*.ts"] },
	async (eventType, filePath) => {
		console.log(`${eventType}: ${filePath}`);
	},
);
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

async function watchFiles(
	sandbox: any,
	path: string,
	options: { include?: string[]; exclude?: string[] },
	handler: (
		eventType: string,
		filePath: string,
		isDirectory: boolean,
	) => Promise<void>,
) {
	const stream = await sandbox.watch(path, options);

	for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
		switch (event.type) {
			case "watching":
				console.log(`Watching ${event.path}`);
				break;
			case "event":
				await handler(event.eventType, event.path, event.isDirectory);
				break;
			case "error":
				console.error(`Watch error: ${event.error}`);
				break;
			case "stopped":
				console.log(`Watch stopped: ${event.reason}`);
				return;
		}
	}
}

// Usage
await watchFiles(
	sandbox,
	"/workspace/src",
	{ include: ["*.ts"] },
	async (eventType, filePath) => {
		console.log(`${eventType}: ${filePath}`);
	},
);
```

### Debounced file operations

Avoid excessive operations by collecting changes before processing:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");
const changedFiles = new Set();
let debounceTimeout = null;

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		changedFiles.add(event.path);

		if (debounceTimeout) {
			clearTimeout(debounceTimeout);
		}

		debounceTimeout = setTimeout(async () => {
			console.log(`Processing ${changedFiles.size} changed files...`);
			for (const filePath of changedFiles) {
				await processFile(filePath);
			}
			changedFiles.clear();
			debounceTimeout = null;
		}, 1000);
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");
const changedFiles = new Set<string>();
let debounceTimeout: ReturnType<typeof setTimeout> | null = null;

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		changedFiles.add(event.path);

		if (debounceTimeout) {
			clearTimeout(debounceTimeout);
		}

		debounceTimeout = setTimeout(async () => {
			console.log(`Processing ${changedFiles.size} changed files...`);
			for (const filePath of changedFiles) {
				await processFile(filePath);
			}
			changedFiles.clear();
			debounceTimeout = null;
		}, 1000);
	}
}
```

### Watch with non-recursive mode

Watch only the top level of a directory, without descending into subdirectories:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

// Only watch root-level config files
const stream = await sandbox.watch("/workspace", {
	include: ["package.json", "tsconfig.json", "vite.config.ts"],
	recursive: false,
});

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		console.log("Configuration changed, rebuilding project...");
		await sandbox.exec("npm run build");
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

// Only watch root-level config files
const stream = await sandbox.watch("/workspace", {
	include: ["package.json", "tsconfig.json", "vite.config.ts"],
	recursive: false,
});

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		console.log("Configuration changed, rebuilding project...");
		await sandbox.exec("npm run build");
	}
}
```

## Stop a watch

The stream ends naturally when the container sleeps or shuts down. There are two ways to stop a watch early:

### Use an AbortController

Pass an `AbortSignal` to `parseSSEStream`. Aborting the signal cancels the stream reader, which propagates cleanup to the server. This is the recommended approach when you need to cancel the watch from outside the consuming loop:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");
const controller = new AbortController();

// Cancel after 60 seconds
setTimeout(() => controller.abort(), 60_000);

for await (const event of parseSSEStream(stream, controller.signal)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
	}
}

console.log("Watch stopped");
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");
const controller = new AbortController();

// Cancel after 60 seconds
setTimeout(() => controller.abort(), 60_000);

for await (const event of parseSSEStream<FileWatchSSEEvent>(
	stream,
	controller.signal,
)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
	}
}

console.log("Watch stopped");
```

### Break out of the loop

Breaking out of the `for await` loop also cancels the stream:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");
let eventCount = 0;

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
		eventCount++;

		// Stop after 100 events
		if (eventCount >= 100) {
			break; // Breaking out of the loop cancels the stream
		}
	}
}

console.log("Watch stopped");
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");
let eventCount = 0;

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		console.log(`${event.eventType}: ${event.path}`);
		eventCount++;

		// Stop after 100 events
		if (eventCount >= 100) {
			break; // Breaking out of the loop cancels the stream
		}
	}
}

console.log("Watch stopped");
```

## Best practices

### Use server-side filtering

Filter with `include` or `exclude` patterns rather than filtering events in JavaScript. Server-side filtering happens at the inotify level, which reduces the number of events sent over the network.

Note

`include` and `exclude` are mutually exclusive. Use one or the other, not both. If you need to watch specific file types while ignoring certain directories, use `include` patterns that match the files you want.

```js
import { parseSSEStream } from "@cloudflare/sandbox";

// Efficient: filtering happens at the inotify level
const stream = await sandbox.watch("/workspace/src", {
	include: ["*.ts"],
});

// Less efficient: all events are sent and then filtered in JavaScript
const stream2 = await sandbox.watch("/workspace/src");
for await (const event of parseSSEStream(stream2)) {
	if (event.type === "event") {
		if (!event.path.endsWith(".ts")) continue;
		// Handle event
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

// Efficient: filtering happens at the inotify level
const stream = await sandbox.watch("/workspace/src", {
	include: ["*.ts"],
});

// Less efficient: all events are sent and then filtered in JavaScript
const stream2 = await sandbox.watch("/workspace/src");
for await (const event of parseSSEStream<FileWatchSSEEvent>(stream2)) {
	if (event.type === "event") {
		if (!event.path.endsWith(".ts")) continue;
		// Handle event
	}
}
```

### Handle errors in event processing

Errors in your event handler do not stop the watch stream. Wrap handler logic in `try...catch` to prevent unhandled exceptions:

```js
import { parseSSEStream } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");

for await (const event of parseSSEStream(stream)) {
	if (event.type === "event") {
		try {
			await handleFileChange(event.eventType, event.path);
		} catch (error) {
			console.error(
				`Failed to handle ${event.eventType} for ${event.path}:`,
				error,
			);
			// Continue processing events
		}
	}

	if (event.type === "error") {
		console.error("Watch error:", event.error);
	}
}
```

```ts
import { parseSSEStream } from "@cloudflare/sandbox";
import type { FileWatchSSEEvent } from "@cloudflare/sandbox";

const stream = await sandbox.watch("/workspace/src");

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {
	if (event.type === "event") {
		try {
			await handleFileChange(event.eventType, event.path);
		} catch (error) {
			console.error(
				`Failed to handle ${event.eventType} for ${event.path}:`,
				error,
			);
			// Continue processing events
		}
	}

	if (event.type === "error") {
		console.error("Watch error:", event.error);
	}
}
```

### Ensure directories exist before watching

Watching a non-existent path returns an error. Verify the path exists before starting a watch:

```js
const watchPath = "/workspace/src";
const result = await sandbox.exists(watchPath);

if (!result.exists) {
	await sandbox.mkdir(watchPath, { recursive: true });
}

const stream = await sandbox.watch(watchPath, {
	include: ["*.ts"],
});
```

```ts
const watchPath = "/workspace/src";
const result = await sandbox.exists(watchPath);

if (!result.exists) {
	await sandbox.mkdir(watchPath, { recursive: true });
}

const stream = await sandbox.watch(watchPath, {
	include: ["*.ts"],
});
```

## Troubleshooting

### High CPU usage

If watching large directories causes performance issues:

1. Use specific `include` patterns instead of watching everything
2. Exclude large directories like `node_modules` and `dist`
3. Watch specific subdirectories instead of the entire project
4. Use `recursive: false` for shallow monitoring

### Path not found errors

All paths must exist and resolve to within `/workspace`. Relative paths are resolved from `/workspace`.

Container lifecycle

File watchers are automatically stopped when the sandbox sleeps or shuts down. If the sandbox wakes up, you must re-establish watches in your application logic.

## Related resources

* [File Watching API reference](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/api/file-watching/) — Complete API documentation and types
* [Manage files guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/manage-files/) — File operations
* [Background processes guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/background-processes/) — Long-running processes
* [Stream output guide](https://docs-durable-objects-instance-replaced-errors.previews.developers.cloudflare.com/sandbox/guides/streaming-output/) — Real-time output handling

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